How secondary tax works

"Secondary tax" has a bad reputation, but it isn't an extra penalty. It just sets a flat rate on your second job so your total income is taxed at roughly the right level.

Why it feels high

Your first job uses the low tax bands (10.5% and 17.5%). By the time a second job's income stacks on top, those low bands are already used up — so the secondary code applies a single higher rate (e.g. S, SH or ST) matched to your combined income. You're not taxed twice; the second job just doesn't get the cheap bands again.

Getting it right

Pick the secondary code that matches your combined annual income. If your codes are off, IRD squares it up at year end — over-taxed means a refund, under-taxed means a bill. To see your real combined position, run both incomes through the comparison tool or the main calculator, and check you're on the right tax code.